Polymer-graphene nanocomposites are often inhomogeneous due to their inherent incompatibility. One way to circumvent this dilemma is to use graphene oxide (GO) as a precursor which opens opportunity for the large-scale production of graphene-based materials due to its cost-effective synthesis and solution processability. To re-establish the electronic properties of graphene, the GO should be reduced. Reduction routes such as chemical and high thermal treatment do not only use toxic chemicals but also are not suitable for plastic electronics. Recently, there is a growing interest on photoreduction of GO as a mild and environmentally friendly method. Light-driven reactions are interesting because they afford spatial and temporal control of the process. For instance, the photoreduction of GO is a promising route for the rapid production of photo-patterned circuits which are attractive for electronics industry.
A considerable number of scientific literature have been reported on this topic. However, most of the techniques described utilize inorganic photoreducers or photocatalysts such as TiO2 and H3PW12O40 which rely on the release of electrons from the catalyst that in turn reduce GO. A downside of this approach is the difficulty of removing the inorganic photocatalyst which affects graphene's properties due to contamination. It is worth-noting that there are reports where a photocatalyst is not needed, however, very long irradiation time of up to 48 hours is required. The flash reduction technique using a photographic camera flash is also attractive. However, since the mechanism of reduction relies on photo-thermal heating, this technique is not amenable to solution-based reduction due to fast heat-transfer to the solvent. In addition, other reports on photoreduction are rather complex because the photoreaction has to be performed in N2 and H2 atmosphere or in vacuum. Hence, the development of a simpler, faster and cost-effective photoreduction technique is still an open challenge.
Carbon nanomaterials decorated with metal nanoparticles have important application in the area of catalysis, sensing, fuel cell and other renewable energy-related applications. Over the decades, carbon supported palladium nanoparticles are widely used for heterogeneous catalysis. More recently however, carbon nanotube or graphene supported metal nanoparticles show promising uses for enhanced gas detection, bio-imaging, electrical conductivity, catalytic performance and antimicrobial efficacy. Based on literature, the grafting of these nanoparticles onto carbon supports are made possible by the oxygen-containing functionalities such as carboxylic, carbonyl and phenolic groups that serve as anchor points of metal nanoparticles. Also, theoretical calculations have shown considerable affinity between metals and pristine graphene and carbon nanotubes. However, very recent experimental reports suggest that metal-carbon interaction is actually covalent in nature.
Graphene-nanoparticle hybrids are commonly prepared by in situ reduction, hydrothermal and electrochemical techniques, and ex-situ methods. One of the challenges of all the in situ techniques is the difficulty to control the size and morphology of the nanoparticle. On the other hand, for ex-situ methods, since the NPs are synthesized beforehand, it allows precise control of the size, shape and density of NP. Of these four, in situ reduction techniques are the most commonly employed method as these are usually one-pot synthetic routes, highly efficient, easily performed and environment-friendly. Though ex situ methods allow for better control of the size distribution of the NP, in situ methods are more explored in literature since the simplicity of the method outweighs the cost, tedious procedure and time-consuming nature of ex situ procedures. The incorporation of these metal nanoparticles on carbon supports usually involves surfactant- or polymer-stabilized nanoparticles which require separate synthetic procedure for the metal nanoparticle. This process is not only tedious but also not environment-friendly since it uses several reagents and solvents in the process of fabricating the material.
It is therefore a problem of the invention to pursue alternatives that are facile, environment-friendly and cost-effective.